Provided by: libx11-doc_1.6.4-3_all bug


       XGetEventData, XFreeEventData, XGenericEventCookie - retrieve and free additional event
       data through cookies.


       Bool XGetEventData(Display *display, XGenericEventCookie *cookie);

       void XFreeEventData(Display *display, XGenericEventCookie *cookie);


       display   Specifies the connection to the X server.

       cookie    Specifies the cookie to free or retrieve the data for.


       typedef struct {
               int type;
               unsigned long serial;
               Bool send_event;
               Display *display;
               int extension;
               int evtype;
               unsigned int cookie;
               void *data;
       } XGenericEventCookie;


       Some extension XGenericEvents require additional memory to store information.  For these
       events, the library returns a XGenericEventCookie with a token ('cookie') unique to this
       event. The XGenericEventCookie's data pointer is undefined until XGetEventData is called.

       The XGetEventData function retrieves this extra data for the given cookie. No round-trip
       to the server is required. If the cookie is invalid or the event is not an event handled
       by cookie handlers, False is returned. If XGetEventData returns True, the cookie's data
       pointer points to the memory containing the event information. A client must call
       XFreeEventData to free this memory.  XGetEventData returns False for multiple calls for
       the same event cookie.

       The XFreeEventData function frees the data associated with a cookie. A client must call
       XFreeEventData for each cookie claimed with XGetEventData.


       XEvent event;
       XGenericEventCookie *cookie = &ev;

       XNextEvent(display, &event);
       if (XGetEventData(display, cookie)) {
       } else
       XFreeEventData(display, cookie);


       A cookie is defined as unclaimed if it has been returned to the client through XNextEvent
       but its data has not been retrieved via XGetEventData.  Subsequent calls to XNextEvent may
       free memory associated with unclaimed cookies.  Multi-threaded X clients must ensure that
       XGetEventData is called before the next call to XNextEvent.


       Xlib - C Language X Interface